Heretofore, a resin duct-integrated floor-raising material is used for adjusting the height of the floor surface of an automobile.
The resin vehicle floor-raising material is in a nearly rectangular panel shape in a predetermined thickness (height) according to the specifications. The raising material is demanded to reduce the weight, and is disposed on the floor pan of the automobile, mainly on the foot of a driver seat. Moreover, since the raising material is demanded to have stiffness, particularly compressed stiffness in that the driver's feet are placed on the top surface, an integrated hollow structure body is adopted in which a rib is disposed in the integrated hollow structure body to extend between a top sidewall and a back sidewall for joining the two walls.
Since such a floor-raising material is a resin integrated hollow structure body, a method for molding the floor-raising material is blow molding, which is more technically advantageous than injection molding. For example, Patent Document 1 discloses a method for producing an automobile floor-raising material by blow molding.
The method for producing an automobile floor-raising material is a method for blow-molding a molten parison in split molds. The manufacture method generally includes the steps of opening the split molds, dropping the molten parison between the opened split molds, and clamping the split molds and blowing a pressurized fluid into the molten parison.
More specifically, the manufacture method is a method for producing an automobile floor-raising material in a hollow double wall structure including a front sidewall and a back sidewall opposite to each other as a gap is spaced. In the manufacture method, first, split molds are opened. The split molds are formed of two molds. One of the molds includes a rib forming portion protruding in a plate shape to form a plurality of groove ribs recessed in grooves on the front sidewall side of an automobile floor-raising material. The other mold includes a rib forming portion protruding in a nearly cone shape to form a plurality of cone ribs recessed in a nearly cone shape on the back sidewall side of the automobile floor-raising material. Subsequently, a molten parison is dropped between the split molds. The split molds are then clamped in such a way that the tip end portion of the rib forming portion of the one mold faces and comes close to the tip end portion of the rib forming portion of the other mold. Subsequently, a pressurized fluid is blown into the parison. Thus, the parison is expanded along a cavity in the split molds, and the groove rib is integrally welded to the cone shaped rib. Thus, the front sidewall is formed with a plurality of groove ribs recessed in grooves nearly in parallel with each other toward the back sidewall. On the other hand, the back sidewall is formed with the cone shaped ribs recessed in a nearly cone shape at positions opposite to the groove ribs toward the front sidewall side. As a result, the automobile floor-raising material is blow-molded in which the top walls of the cone shaped ribs and the tip end portions of the groove ribs integrally form welded portions.
Generally, an air duct is disposed near the foot of the driver seat in order to flow air-conditioned air from an air conditioner disposed on the front part of the automobile to the rear seat of the automobile. The air duct extends in the vehicle longitudinal direction across the adjacent edge portions of the resin vehicle floor-raising material disposed on the foot of the driver seat or across the opposite edge portions.
On this point, Patent Document 2, for example, discloses a duct-integrated floor-raising material in which an air duct and a floor-raising material are integrally formed in a module and the number of parts is reduced. This duct-integrated floor-raising material is made of a resin, and has a hollow double wall structure formed of a top sidewall and a back sidewall. Moreover, in the duct-integrated floor-raising material, a first recessed groove and a second recessed groove protruding from the back sidewall to the hollow portion side are integrally formed at a welded portion with respect to the top sidewall. Thus, a duct portion is disposed between the first recessed groove and the second recessed groove, and the duct portion includes an air channel separated from the hollow portion of the floor-raising material.
In the case where such a duct-integrated floor-raising material is integrally molded by blow molding as in Patent Document 1, a blow pin should be pierced into a molten parison for applying a blowing pressure, resulting in the following technical problems.
First, a defective product is produced depending on the position to pierce the blow pin.
More specifically, as discussed above, the duct extends in the vehicle longitudinal direction across the adjacent edge portions of the duct-integrated floor-raising material or the opposite edge portions. Thus, the duct-integrated floor-raising material is formed with three hollow portions partitioned from each other. One of the hollow portions is a duct forming an air channel. In the duct-integrated floor-raising material, the hollow portion is divided unequally as compared with a typical duct. Therefore, the divided hollow portions include a single large hollow portion, a single small hollow portion, and a duct forming an air channel and formed between the large hollow portion and the small hollow portion. In this case, the hollow portions other than the duct are not demanded to have strict-sealing properties as long as a predetermined stiffness is maintained. The reason is that even though the mark (a hole) of the blow pin is left and the sealing properties are not secured, originally, a carpet is laid on the top surface of the duct-integrated floor-raising material. Thus, the beauty of the appearance is not demanded, thereby securing the heights of the hollow portions, or the thickness of the floor-raising material.
However, the duct portion is an air conditioning air channel. Thus, when the mark (a hole) of the blow pin is left, air is leaked from the mark to cause a reduction in ventilation efficiency. With the reduction in ventilation efficiency, an unusual sound sometimes occurs from the floor surface in leaking air.
The duct portion may be separately molded (for example, the duct portion is blow-molded) and prepared as a molded component in order to maintain the performance or the quality of a duct. However, the floor-raising material is blow-molded without the duct portion, and the duct portion is later assembled. Thus, the manufacture efficiency of the floor-raising material can be degraded.
Secondly, since there are a larger number of blow pins, the circulation of blowing air is poor, which adversely affects the molding properties.
More specifically, in the case where blow pins are pierced to three hollow portions partitioned from each other for blow-molding, it is necessary to increase the number of blow pins to pierce according to the volumes of the hollow portions from the viewpoint of molding efficiency. However, on the contrary, an increased number of blow pins sometimes degrade the circulation of blowing air in the hollow portions. As a result, the molding properties of the molten parison molded by a blowing pressure are sometimes degraded.
Thirdly, the improvement of the sound insulation properties of the duct portion in which ventilating air flows is restricted.
More specifically, in order to improve the sound insulation properties of the duct portion, it is necessary to increase the volume of the hollow portion in the duct portion. However, in the case of the duct-integrated floor-raising material, the duct portion is disposed between the small hollow portion and the large hollow portion, and has a limitation on the expanse. On the other hand, it is inevitable to restrict the volume of the hollow portion in the duct portion of the duct-integrated floor-raising material. This is because the height of the duct portion is generally set lower than the heights of the small hollow portion and the large hollow portion because a driver, for example, steps on the top surface of the duct portion. Moreover, the duct portion between the small hollow portion and the large hollow portion is formed to be protected by the adjacent small hollow portion and the adjacent large hollow portion with stiffness. As a result, an air passing sound is sometimes noticeable, which comes from the duct portion of the duct-integrated floor-raising material disposed on the foot of the driver seat.
Fourthly, it is difficult to secure molding efficiency without impairing a weight reduction.
More specifically, in the case where blow pins are pierced to the large hollow portion, the small hollow portion, and the duct portion to mold the portions by blow molding, it is possible to achieve a weight reduction by individually forming hollow portions in the large hollow portion, the small hollow portion, and the duct portion. However, it is difficult to secure molding efficiency. In this case, a hollow portion should be disposed as an air channel in the duct portion. However, the large hollow portion or the small hollow portion may be entirely formed in a solid without blow molding because of no need to provide a hollow portion in the large hollow portion or the small hollow portion. However, when the large hollow portion or the small hollow portion is formed in a solid entirely, it does not considerably contribute to reducing the weight because the heights of the hollow portions are used for raising the floor.    Patent Document 1: Japanese Patent No. 4462924    Patent Document 2: JP-A-2010-30553